1. Field of the Invention
The present invention relates to a method of inspecting a sample by irradiating it with a primary beam, such as a charged-particle beam, via a film and detecting a secondary signal emanating from the sample in response to the irradiation. Furthermore, the present invention relates to a sample inspection apparatus adapted for use in this method. The present invention also relates to a sample holder adapted to be used in this method.
2. Description of Related Art
In a sample inspection apparatus incorporating the facilities of a scanning electron microscope (SEM), a sample to be investigated is normally placed within a sample chamber whose inside has been evacuated by means of pumping. The sample placed in the sample chamber that is in the reduced pressure ambient is irradiated with a primary beam, such as a charged-particle beam (e.g., an electron beam). As a result, various secondary signals, such as backscattered electrons, secondary electrons, fluorescence, and X-rays, are produced from the sample. Any kind of the secondary signals is detected, and an image of the sample is created based on the detected signal. Thus, the sample is inspected.
Accordingly, when the sample under inspection contains moisture, it is necessary to prevent evaporation of the moisture from the sample. Consequently, it is necessary to prevent the sample from being exposed to the reduced pressure ambient within the sample chamber.
One conceivable method of inspecting a sample by SEM without exposing the sample to such a reduced pressure ambient consists of preparing a sample holder having an aperture that has been closed off by a film, placing the sample in the holder, and placing the holder within the SEM sample chamber that is in a reduced pressure ambient.
The inside of the sample holder in which a sample is placed is not evacuated. The film that covers the opening formed in the sample holder can withstand the pressure difference between the reduced pressure ambient in the SEM sample chamber and the non-evacuated ambient (e.g., atmospheric-pressure ambient) inside the sample holder. Also, the film permits transmission of an electron beam (see, for example, JP-T-2004-515049).
When a sample is inspected, an electron beam is directed from outside the sample holder at the sample placed in the holder via the film on the sample holder disposed in the SEM sample chamber that is in a reduced-pressure ambient. Backscattered electrons are emitted from the irradiated sample. The electrons penetrate through the film on the sample holder and are detected by a detector mounted in the SEM sample chamber. As a result, an SEM image of the sample is obtained.
Another example in which a sample is irradiated with an electron beam via a film withstanding the pressure difference between vacuum and atmospheric pressure and an SEM image is derived by detecting backscattered electrons emitted from the sample is described in Atmospheric scanning electron microscopy, Green, Evan Drake Harriman, Ph. D., Stanford University, 1993 (especially, Chapter 1: Introduction).
It is also possible to form a pair of opposite films from the above-described film. A sample is placed between the films, and a TEM (transmission electron microscope) image can be obtained. This technique is described in JP-A-47-24961 and JP-A-6-318445. Especially, in JP-A-47-24961, a case where an SEM image of the sample placed between such a pair of films is obtained is described.
In the above-described specimen inspection procedure, a primary beam, such as an electron beam, is directed at the sample via a film. A secondary signal, such as backscattered electrons, emitted from the sample in response to the irradiation is detected, and the sample is inspected.
In this inspection procedure, it is necessary to prepare a different sample holder for each kind of sample. Therefore, the sample holders used in this sample inspection are preferably inexpensive.